Scanning antenna



March 31, 1953 v, RQBINSQN 2,633,533

SCANNING ANTENNA Filed Aug. 1, 1945 INVENTOR CHARLES V. ROBINSONATTORNEY Patented Mar. 31, 1953 Charles V. Robinson, Newton Center,Mass., as-

signor, by mesne assignments, to the United States of America as r taryof War epresented by the Secre- Application August 1, 1945, Serial No.608,299

This invention relates to antenna systems and particularly to such meansadapted to radiate or intercept electromagnetic waves in a desireddirection.

object of this invention is to provide improved means for scanning asector of space with electromagnetic radiation at a high rate withoutmechanical movement of the entire antenna.

Otherobjects, advantages, and novel features of the invention willappear more fully herein.

, In the drawings:

Fig. 1 illustrates in plan a preferred embodiment of the invention;

Fig. 2 is a perspective view of a wave guide contemplated for use in theapparatus of Fig. 1; Figure 3 is a sectional view of the waveguide ofFigure 2 taken along the line 33 of Figure 2, including also a partialsectional view of the end of one of the waveguides ID of Figure l.- a

Wave guides l extend radially from arotating joint I l to whichelectromagnetic energy is'fed from a suitable source, The rotating jointIl may include switching means suchas disclosed in the application ofLan J. Chu, Ivan A. Getting, and Henry A. Strauss, Serial No. 535,856,filed May 16, 1944 Patent No. 2,549,721 granted April 17, 1951.Apertures [2 at the outer termini of wave guides ware closed by lensesI3 composed of polystyrene or other material refractive toelectromagnetic radiation. Wave guides ID, are rotatable about axis M.The rotating joint ll may also include any well known means, for examplea motor, for causing waveguides I0 to rotate about axis M. It is to beunderstood, of course, that the inventionis not limited to a motorlocated within rotating joint ll since the method 'of rotatingwaveguides Ill about axis 14 is a matter of design and mechanicalexpediency. Electromagnetic energy may be fed through wave guides Illandlenses l3 into semi-circular aperture l5 of wave guide I8, Figs. 1 and2, of the pill-box type. The energy then passes through wave guide 18and is emitted from an aperture 16. at the extremity thereof. Theswitching means above-mentioned may be adapted to permit each wave guideIt to transmit energy only when it lies within the sector of 90 betweenlines ll, each of which is disposed at a 45 angle with respect to theline of aperture l6. Wave guide I8 is formed of two members l9 andaffording conductive, substantially parallel surfaces preferablyseparated by less than one-half wave length near the mid-frequency ofthe proposed band of operating frequencies, and the median surfacerepresented by the dashed line 40mins. (o1.2s0 es.ss)

' 2| of Figure ,3 lying between the two conductive surfaces, at leastfor a portion of its extent, is in the shape of a surface of revolutionsuch as a toroid. For reasons of clarity, median surface defined above.

Because of the semi-circular shape of wave guide l8 unequal path lengthsare presented to the plane of the energy propagated into it from waveguide It and therefore the phase front of I the wave which is emittedfrom aperture IS, in the absenceof lenses [3, has the'shape of a curvedplane. In this connection reference is made to co-pending application ofLan J. Chu and Charles V. Robinson, 'Serial No. 608,298, filed August 1,

1945, in which the wavefront which emanates from. such an apparatus isconsidered without regard to a corrective lenssuch as here employed:

The purpose of lenses I3 is to correct the curvature of the phase front,and cause a straight line phase front to emanate from aperture l6; By astraight line phase front is meant that the plane of the phase front ofthe emitted wave is fiat. The lenses l3 compensate in advance of waveguide l8 for the effects produced on the radiated wave front by theunequal path lengths of wave guide l8. Various methods might be employedto calculate the necessary shape of the lens having a knowledge of therefractive index of the material with which it is to be made. The shapeof the lenses l3 may also be determined by graphical methods applyingwell known optical principles.

'The use of lenses does not require the choice of a particular size oroptimum ratio of dimensions of thewave guide for a desired approach to astraight line phase front. Therefore, the

height of the median surface of revolution of wave guide 18 may beconsiderably reduced, thereby reducing the weight and the size of thestructure and providing a more compact apparatus. Furthermore, lenses I3may be relatively thin, and dielectric losses are consequently small. Itshould now be apparent from the foregoing description of the inventionthat as wave guides 10 rotate about axis l4 energy radiated fromaperture I6 is caused to scan a sector in space in a plane perpendicularto axis I 4. Stated in another way, suppose wave guides ID in Figure 1rotate clockwise about axis I4 at a predetermined rate of speed. In thiscase when one of wave guides I0 just enters the sector defined by linesI1 energy is supplied to this wave guide.

radiated through orifice l6 backward in the di- With the wave guide inthis position, the direction of the" rection of the exciting wave guide.

major lobe of the radiated wave or the maximum end waveguide rotatableabout the axis of said in the space energy pattern will lie to the righti of the normal to aperture i6 as seen Figure 1. As wave guide I!) movesclockwise to the position shown in Figure 1 the direction of the maximumwill move toward the normal to aperture 16 and as wave guide l0 advancesbeyond the position" shown in Figure 1 the direction of the maximum inthe space energy pattern will move to the left of the normal to apertureI 6 as seen in Figure 1. Since the wave emitted from aperture it has aplanar phase front because of the effects of lenses [3, the emitted waveis' highly direc' tional.

. It should be obvious from the geometry of Figure 1 that as one'of waveguides It moves out of the sector defined by lines I! another wave guideenters this sector so that the scanningcycle is repeated. I

: fit-should be further noted here that during the scan ing cycle. theonly parts of the antenna thatmove' are wave guides H1 and rotatingjointfl. Sincethese parts are. light in weight and are arrangedsymmetrically about axis M, they may be rotated at relatively high speedwithout difiiculty. This results; in a much faster wide; angle, scanthan was heretofore possible.

For a more, detailed explanation of the theory of how the energyradiated from stationary aperture [8. is caused to scan a sector inspace reference is again made to the copending application 01 Lan JenChu and Charles V. Robinson.

Although the discussion herein has been directed to' the. transmissionof energy from a source, a converse effect permits the same structure tobe used in the reception of radiation with similar directive properties,as is well known in the art.-

Many variations of the invention will be apparent to those skilled inthe art and it is therefore not desired to restrictv the scope of theclaims tov the precise embodiment as herein disclosed.

I What is claimed is;

1. An apparatusfor scanning a sector of space with electromagneticradiation including a first wave guide formed of two members, providingconductive substantially parallel surfaces, said members being so shapedthat the median surface between said parallel surfacesv comprisessubstantially a portion of a surface of revolution, a movable wave guidfor transmitting electromagnetic radiation to said first wave. guide,and a lens closing said movable; wave guide, said lens being formed ofmaterial refractive to said radiation and so shaped that when saidradiation is fed through said movable wave guide the radiation emanatingfrom said first wave guide shall have a planar phase front.

2. An apparatus for scanning a sector of space with electromagneticradiations including a first waveguide formed of two members providinconductive substantially parallel surfaces, said members being so shapedthat the median surface between said parallel surfaces comprises substantially a portion of a surface of revolution, a sec- ,surface ofrevolution, and a lens interposed between said first and secondwaveguide and rotatable with said second waveguide, said lens beingformed. of material refractive to said radiation and shaped to alter thepath of energy passing between said two waveguides to determine thephasefront of the energy radiated from said first waveguide.

3. An apparatus for scanning a sector of space with electromagneticradiations including afirst waveguide formed of two members providingcon ductive substantially parallel surfaces, said members bein so shapedthat the median surface be tween said parallel surfaces comprisessubstana tiallya portion of a surface of revolution, 2. second waveguiderotatable about the axis of said surface of revolution, and aconcave-convex lens interposed between said first and second wave-.guide and rotatable with said second Waveguide. said lens being. formedof material; refractive to said radiation and shaped to correct thespherical aberration of said first waveguide to cause the energy that isradiated from said first waveguide to have aplanar phase front.

4. An antenna. for scanning a sector in space comprising a firstwaveguide having an input section in the form of half an annulus, anoutput section in the form of a half circle having the same axis and thesame circumference as said input section, and a U-shaped section joiningsaid input and output section; a second waveguide rotatable about theaxis of said first waveguide and positioned to propagate electromagneticenergy into said input section, and a lens.

carried in the end of said second Wave uide proximal to said firstwaveguide, said lens being formed of a material refractive toelectromagnetic energy and shaped to correct for wavefront distortionscaused by said first waveguide in the wave radiated from said outputsection.

CHARLES V. RQBINSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES. PATENTS Number Name Date 2,202,380 Hollman May 28, 194,02,283,568 om May-19,1942 2,283,935 King May 26, 1942 2,405,242Southworth Aug, 6, 1946 2,434,253 Beck Jan. 13, 1948

